Method of producing an abrasive product containing cubic boron nitride

ABSTRACT

A method of producing an abrasive product consists of providing a mixture of a mass of discrete carbide particles and a mass of cubic boron nitride particles, the cubic boron nitride particles being present in the mixture in an amount such that the cubic boron nitride content of the abrasive product is 25% or less by weight, and subjecting the mixture to elevated temperature and pressure conditions at which the cubic boron nitride is crystallographically stable and at which substantially no hexagonal boron nitride is formed, in the presence of a bonding metal or alloy capable of bonding the mixture into a coherent, sintered product, to form the abrasive product. The bonding metal or alloy comprises a combination of a transition metal or a transition alloy and up to 40% by volume of the bonding metal or alloy of a second metal which is a stronger nitride or boride former than the transition metal or the transition metal alloy.

BACKGROUND TO THE INVENTION

This invention relates to a method of producing an abrasive productcontaining cubic boron nitride and cemented carbide.

Cemented carbide is a material which is used extensively in industry fora variety of applications, both as an abrading material and as a wearresistant material. Cemented carbides generally consist of suitablecarbide particles such as tungsten carbide, tantalum carbide or titaniumcarbide, bonded together by means of a bonding metal such as cobalt,iron or nickel, or an alloy thereof. Typically, the metal content ofcemented carbides is about 3 to 35% by weight. They are produced bysintering the carbide particles and the bonding metal at temperatures ofthe order of 1400° C.

At the other end of the spectrum, ultrahard abrasive and wear resistantproducts are found. Diamond and cubic boron nitride compacts arepolycrystalline masses of diamond or cubic boron nitride particles, thebonding being created under conditions of elevated temperature andpressure at which the ultrahard component, i.e the diamond or cubicboron nitride, is crystallographically stable. Polycrystalline diamond(PCD) and polycrystalline cubic boron nitride (PCBN) can be producedwith or without a second phase or bonding matrix. The second phase, whenprovided, may be, in the case of diamond, a catalyst/solvent such ascobalt, or may be a carbide forming element such as silicon. Similarsintering mechanisms are utilised in PCBN synthesis with variouscarbides, nitrides and borides being common second phases.

PCD and PCBN have a far higher wear resistance than cemented carbides,but tend to be somewhat brittle. This brittleness can lead to edgechipping of the working surface which can present a problem inapplications where fine finishes are required. Furthermore, ultrahardproducts such as PCD and PCBN can generally not be directly brazed ontoa metallic support. They are therefore often sintered in combinationwith a cemented carbide substrate. The bi-layered nature of suchultrahard products can be problematic in terms of thermo-mechanicalstresses between the two materials: differential expansion and shrinkageon heating and cooling due to different thermal expansion coefficientsand elastic moduli can lead to crack formation or unfavourable residualstresses if the substrate and the ultrahard products are too dissimilar.Another potential problem of such bi-layered materials is that ofundercutting, i.e. preferential wear of the less abrasion resistantcarbide support. Further, machining of ultrahard products is difficultand costly, where carbide products can be relatively easily ground tothe final geometry.

Efforts have been made to solve some of these problems.

JP-A-57 116 742 discloses the preparation of a modified cemented carbideunder hot pressing conditions, i.e. temperatures of the order of 1400°C. to 1500° C. with little or no pressure being applied. These are notconditions at which cubic boron nitride is crystallographically stable.

European Patent No 0 256 829 describes a method of producing an abrasiveand wear resistant material comprising a mass of carbide particles, amass of cubic boron nitride particles and a bonding metal or alloybonded into a coherent, sintered form, the cubic boron nitride particlecontent of the material not exceeding 20% by weight and the materialbeing substantially free of hexagonal boron nitride, which comprisescontacting appropriate amounts of a mass of carbide particles and a massof cubic boron nitride particles with a bonding metal or alloy andsintering the particles and metal or alloy under temperature andpressure conditions at which the cubic boron nitride iscrystallographically stable.

SUMMARY OF THE INVENTION

According to the invention there is provided a method of producing anabrasive product comprising:

-   -   (1) providing a mixture of a mass of discrete carbide particles        and a mass of cubic boron nitride particles, the cubic boron        nitride particles being present in the mixture in an amount such        that the cubic boron nitride content of the abrasive product is        25% or less by weight; and    -   (2) subjecting the mixture to elevated temperature and pressure        conditions at which the cubic boron nitride is        crystallographically stable and at which substantially no        hexagonal boron nitride is formed, in the presence of a bonding        metal or alloy capable of bonding the mixture into a coherent,        sintered product, wherein the bonding metal or alloy comprises a        combination of:        -   (a) a transition metal or a transition metal alloy,            preferably cobalt, iron or nickel, or alloys thereof; and        -   (b) from greater than 0% up to 40% by volume of the bonding            metal or alloy (i.e. metal (a) plus metal (b)) of a second            metal which is a stronger nitride and/or boride former than            the transition metal or the transition metal alloy, or an            alloy of the second metal;    -   to produce the abrasive product.

The metal (b) is preferably selected from the group consisting ofaluminium, silicon, titanium, zirconium, molybdenum, niobium, tungsten,vanadium, hafnium, tantalum, chromium, magnesium, calcium, barium,ytrium, beryllium, cerium, strontium, thorium, lanthanum and lithium.

The preferred metal (b) is selected from the group consisting ofsilicon, aluminium and titanium.

Preferably, the bonding metal or alloy comprises from 60% to 99.5% byvolume of the metal (a) and from 0.5% to 40% inclusive by volume of themetal (b).

The metal (a) is preferably provided in powdered form, but may also beadded in the form of an organic precursor or salt precursor that issubsequently pyrolised to result in finely dispersed metal.

The metal (b) may be provided in powdered form but may also be added inthe form of an organic precursor or salt precursor. Additionally, themetal (b) may be provided in the form of a non-stoichiometric carbide,nitride or boride or in the form of a stoichiometric carbide, nitride orboride where this is sufficiently soluble in the metal (a) such thatmetal (b) can migrate through metal (a).

The metals (a) and (b) may also be provided in the form of an alloy ofthe metals (a) and (b).

The bonding metal or alloy, e.g. the metals (a) and (b) may be mixedwith the carbide particles and with the cubic boron nitride particlesand the mixture may then be sintered as such, or the mixture may firstbe cold-pressed to produce a weak but coherent body prior to sintering.

Alternatively, the bonding metal or alloy, e.g. the metals (a) and (b)may be supplied in the form of a separate layer adjacent to the cubicboron nitride-carbide mixture and infiltrated during the hightemperature/high pressure treatment step.

The cubic boron nitride particles are preferably present in the mixturein an amount such that the cubic boron nitride content of the abrasiveproduct is from 10% to 18% inclusive by weight.

The cubic boron nitride particles may be fine or coarse. The cubic boronnitride particles preferably have a particle size in the range of from0,2 μm to 70 μm inclusive, preferably less than 20 μm, more preferablyless than 10 μm.

The bonding metal or alloy is preferably used in an amount of from 2% to20% inclusive by weight of the abrasive product, more preferably from 5%to 20% inclusive by weight of the abrasive product, most preferably lessthan 15% by weight of the abrasive product.

The carbide particles may be any carbide particles used in themanufacture of conventional cemented carbides. Examples of suitablecarbides are tungsten carbide, tantalum carbide, titanium carbide andmixtures of two or more thereof.

The carbide particles preferably have a particle size in the range offrom 0,1 μm to 10 μm inclusive.

The sintering of the mixture of carbide and cubic boron nitrideparticles and the bonding metal or alloy preferably takes place at atemperature in the range of from 1200° C. to 1600° C. inclusive, and ata pressure from 30 to 70 kbar inclusive.

This step is preferably carried out under controlled non-oxidisingconditions.

The sintering of the mixture of carbide and cubic boron nitrideparticles and the bonding metal or alloy may be carried out in aconventional high temperature/high pressure apparatus. The mixture maybe loaded directly into the reaction capsule of such an apparatus.Alternatively, the mixture may be placed on a cemented carbide supportor a recess formed in a carbide support, and loaded in this form intothe capsule.

In a preferred method of the invention, the carbide particles, the cubicboron nitride particles and the bonding metal or alloy have volatilesremoved from them prior to sintering, e.g. by heating them in a vacuum.These components are preferably then vacuum sealed by, for example,electron beam welding prior to sintering. The vacuum may, for example,be a vacuum of 1 mbar or less and the heating may be a temperature inthe range of 500° C. to 1200° C. inclusive.

The abrasive product produced by the method of the invention may be usedas an abrasive product for abrading materials, or as a wear resistantmaterial, particularly in tool components or inserts which consist of anabrasive compact bonded to a cemented carbide support. Typicalapplications include the cutting of wood and construction materials aswell as the machining of various metallic work pieces such as stainlesssteel, nodular cast irons and superalloys.

DESCRIPTION OF EMBODIMENTS

The crux of the invention is a method of producing an abrasive productby providing a mixture of a mass of discrete carbide particles and amass of cubic boron nitride particles, and subjecting the mixture toelevated temperature and pressure conditions at which the cubic boronnitride is crystallographically stable and at which substantially nohexagonal boron nitride is formed, in the presence of a bonding metal oralloy capable of bonding the mixture into a coherent, sintered product.The cubic boron nitride particles are present in the mixture in anamount such that the cubic boron nitride content of the abrasive productis 25% or less by weight, preferably in the range of from 10% to 18%inclusive by weight.

The bonding metal or alloy comprises a combination of:

-   -   (a) a transition metal or a transition metal alloy, preferably        cobalt, iron or nickel, or alloys thereof;    -   (b) from greater than 0% up to 40% by volume of the bonding        metal or alloy of a second metal which is a stronger nitride or        boride former than the transition metal or transition metal        alloy, or an alloy of the second metal.

The abrasive product produced is, in effect, a cemented carbide whichhas been modified by the addition of cubic boron nitride particles. Theaddition of these particles provides the cemented carbide with greaterabrasive and wear resistant properties.

The abrasive product produced must be substantially free of hexagonalboron nitride. The presence of any significant quantity of hexagonalboron nitride reduces the abrasive wear resistant properties of theproduct. In producing the product, it is important that conditions arechosen which achieve this.

The sintering step is carried out in the presence of a bonding metal oralloy which comprises a combination of (a) a transition metal ortransition metal alloy and (b) from greater than 0% up to 40% by volumeof the bonding metal or alloy of a second metal which is a strongernitride or boride former than the transition metal or transition metalalloy, or an alloy of this second metal.

As the boride or nitride forming metals tend to react with the cubicboron nitride particles, high amounts of such metals can result inexcessive loss of the cubic boron nitride phase and the formation of ahigh proportion of undesirable brittle phases. Thus, metal (b) is usedin an amount up to 40% by volume of the bonding metal or alloy, i.e. thetotal metal content, and this has been found sufficient to achieve ahighly wear resistant product.

The presence of the metal (b) leads to improved bonding of the cubicboron nitride grains to the carbide matrix and thus to an improvement inthe properties of the abrasive product produced.

The invention will now be described in more detail with reference to thefollowing examples.

EXAMPLE 1 (COMPARATIVE EXAMPLE)

A powder mixture of 10,6 wt % cubic boron nitride, 79,6 wt % tungstencarbide and 9,8 wt % cobalt, all in the size range 1 to 2 micron, wasthoroughly mixed in a planetary ball mill to achieve a homogeneous blendof the materials. The blend was uniaxially compacted to form a coherentpellet. The pellet was loaded into a metal canister and subsequentlyoutgassed under vacuum at 1100° C. and sealed by electron beam welding.The sealed containers were loaded into the reaction capsule of astandard high pressure/high temperature apparatus and the loadedcapsules placed into the reaction centre of this apparatus. The contentsof the capsule were exposed to a temperature of approximately 1450° C.and a pressure of 50 kbar. These conditions were maintained for 10minutes. After completion of the treatment a well-sintered, hard andwear resistant material was recovered from the canister.

The abrasion resistance of the material was tested using a turning testwhere silica flour filled epoxy resin was machined using the followingconditions:

Sample format: 90° quadrant 3.2 mm thick Tool holder: neutral Rateangle: 0° Clearance angle: 6° Cutting speed: 10 m/min Depth of cut: 1.0mm Feed rate: 0.3 mm/rev Test duration: 60 s

Under the given conditions the material exhibited a maximum flank wearwidth of 0,17 mm.

EXAMPLE 2

In order to assess the benefit of a nitride and boride forming additivethe following mix was prepared using the method of Example 1:

-   -   10,6 wt % cubic boron nitride    -   79,6 wt % tungsten carbide    -   9,2 wt % cobalt    -   0,6 wt % aluminium

Using the same turning test as in Example 1 the material showed amaximum flank wear width of 0,14 mm.

1. A method of producing an abrasive product comprising the steps of:(1) providing a mixture including a mass of discrete carbide particlesand a mass of cubic boron nitride particles, the cubic boron nitrideparticles being present in the mixture in an amount such that the cubicboron nitride content of the abrasive product is 25% or less by weight;and (2) subjecting the mixture to elevated temperature and pressureconditions at which the cubic boron nitride is crystallographicallystable and at which substantially no hexagonal boron nitride is formed,in the presence of a bonding metal or alloy capable of bonding themixture into a coherent, sintered product, wherein the bonding metal oralloy comprises a combination of: (a) a transition metal or a transitionmetal alloy; and (b) from greater than 0% up to 40% by volume of thebonding metal or alloy of a second metal which is not a carbide and is astronger nitride or boride former than the transition metal or thetransition metal alloy, or an alloy of the second metal; to produce theabrasive product.
 2. A method according to claim 1 wherein thetransition metal is selected from the group consisting of cobalt, iron,nickel, and combinations thereof.
 3. A method according to claim 1wherein the second metal (b) is selected from the group consisting ofaluminium, silicon, titanium, zirconium, molybdenum, niobium, tungsten,vanadium, hafnium, tantalum, chromium, magnesium, calcium, barium,yttrium, beryllium, cerium, strontium, thorium, lanthanum, lithium, andcombinations thereof.
 4. A method according to claim 3 wherein thesecond metal (b) is selected from the group consisting of silicon,aluminium, titanium, and combinations thereof.
 5. A method according toclaim 1 wherein the bonding metal or alloy comprises from 60% to 99.5%inclusive by volume of the metal (a) and from 0.5% to 40% inclusive byvolume of the metal (b).
 6. A method according to claim 1 wherein themetal (a) is provided in a form selected from powdered form and the formof an organic precursor or salt precursor that is subsequent pyrolisedto result in finely dispersed metal.
 7. A method according to claim 1wherein the metal (b) is provided in a form selected from powder form;the form of an organic precursor or salt precursor; the form of anon-stoichiometric nitride or boride; and the form of a stoichiometricnitride or boride in the metal (a).
 8. A method according to claim 1wherein the metal (a) and the metal (b) are provided in the form of analloy of the metal (a) with the metal (b).
 9. A method according toclaim 1 wherein in step (1) the bonding metal or alloy is mixed with thecarbide particles and with the cubic boron nitride particles, and instep (2) the mixture is subjected to the elevated temperature andpressure conditions.
 10. A method according to claim 1 wherein in step(1) the bonding metal or alloy is mixed with the carbide particles andwith the cubic boron nitride particles, and the mixture is cold-pressedto produce a weak coherent body, and in step (2) the weak coherent bodyis subjected to the elevated temperature and pressure conditions.
 11. Amethod according to claim 1 wherein in step (1) the bonding metal oralloy is supplied in the form of a separate layer adjacent to themixture of the mass of carbide particles and the mass of cubic boronnitride particles, and in step (2) the bonding metal or alloy isinfiltrated when the mixture is subjected to the elevated temperatureand pressure conditions.
 12. A method according to claim 1 wherein thecubic boron nitride particles are present in the mixture in an amountsuch that the cubic boron nitride content of the abrasive product isfrom 10% to 18% inclusive by weight.
 13. A method according to claim 1wherein the cubic boron nitride particles have a particle size in therange of from 0.2 μm to 70 μm inclusive.
 14. A method according to claim1 wherein the bonding metal or alloy is used in an amount of from 2% to20% inclusive by weight of the abrasive product.
 15. A method accordingto claim 1 wherein the carbide particles are selected from the groupconsisting of tungsten carbide particles, tantalum carbide particles,titanium carbide particles, and mixtures of two or more thereof.
 16. Amethod according to claim 1 wherein the carbide particles have aparticle size in the range of from 0.1 μm to 10 μm inclusive.
 17. Amethod according to claim 1 wherein in step (2) the elevated temperatureand pressure conditions are a temperature in the range of from 1200° C.to 1600° C. inclusive and a pressure of from 30 kbar to 70 kbarinclusive.
 18. A method according to claim 1 wherein step (2) is carriedout under controlled non-oxidising conditions.
 19. A method according toclaim 2 wherein the second metal (b) is selected from the groupconsisting of aluminium, silicon, titanium, zirconium, molybdenum,niobium, tungsten, vanadium, hafnium, tantalum, chromium, magnesium,calcium, barium, yttrium, beryllium, cerium, strontium, thorium,lanthanum, lithium, and combinations thereof.
 20. A method according toclaim 19 wherein the second metal (b) is selected from the groupconsisting of silicon, aluminium, titanium, and combinations thereof.21. A method according to claim 20 wherein the bonding metal or alloycomprises from 60% to 99.5% inclusive by volume of the metal (a) andfrom 0.5% to 40% inclusive by volume of the metal (b).
 22. A methodaccording to claim 21 wherein the cubic boron nitride particles arepresent in the mixture in an amount such that the cubic boron nitridecontent of the abrasive product is from 10% to 18% inclusive by weight.23. A method according to claim 22 wherein the cubic boron nitrideparticles have a particle size in the range of from 0.2 μm to 70 μminclusive.
 24. A method according to claim 23 wherein the bonding metalor alloy is used in an amount of from 2% to 20% inclusive by weight ofthe abrasive product.
 25. A method according to claim 24 wherein thecarbide particles are selected from the group consisting of tungstencarbide particles, tantalum carbide particles, titanium carbideparticles, and mixtures of two or more thereof.
 26. A method accordingto claim 25 wherein the carbide particles have a particle size in therange of from 0.1 μm to 10 μm inclusive.
 27. A method of producing anabrasive product comprising: (1) providing a mixture including discretecarbide particles and cubic boron nitride particles, the cubic boronnitride particles being present in an amount such that the abrasiveproduct has a cubic boron nitride content of about 10-18% by weight; and(2) subjecting the mixture to elevated temperature and pressureconditions at which the cubic boron nitride is crystallographicallystable and at which substantially no hexagonal boron nitride is formed,in the presence of a bonding metal or alloy which comprises acombination of: (a) a first metal selected from the group consisting ofa transition metal and a transition metal alloy; and (b) from 05% up to40% by volume of the bonding metal or alloy of a second metal which isnot a carbide and is selected from the group consisting of aluminum,silicon, titanium, zirconium, molybdenum, niobium, tungsten, vanadium,hafnium, tantalum, chromium, magnesium, calcium, barium, yttrium,beryllium, cerium, strontium, thorium, lanthanum, lithium, and alloysthereof; to produce the abrasive product.
 28. The method of claim 27,wherein the transition metal is selected from the group consisting ofcobalt, iron, nickel, and combinations thereof.
 29. The method of claim27, further comprising the step of providing the first metal in powderedform.
 30. The method of claim 27, further comprising the step ofproviding the first metal in the form of a pyrolised organic precursoror salt precursor.
 31. The method of claim 27, further comprising thestep of providing the second metal in powdered form.
 32. The method ofclaim 27, further comprising the step of providing the second metal inthe form of an organic precursor or salt precursor.
 33. The method ofclaim 27, further comprising the step of providing the second metal inthe form of a nitride or boride that is soluble in the first metal. 34.The method of claim 27, wherein the elevated temperature is about1200-1600° C.
 35. The method of claim 27, wherein the elevated pressureis about 40-70 kbar.
 36. The method of claim 27, wherein the carbideparticles are selected from the group consisting of tungsten carbideparticles, tantalum carbide particles, titanium carbide particles, andcombinations thereof.
 37. The method of claim 27, wherein the bondingmetal or alloy constitutes about 2-20% by weight of the abrasiveproduct.
 38. A method of producing an abrasive product comprising: (1)providing a mixture including carbide particles having a particle sizeof about 0.1-10 microns and cubic boron nitride particles having aparticle size of about 0.2-70 microns, the cubic boron nitride particlesbeing present in an amount such that the abrasive product has a cubicboron nitride content of up to about 25% by weight; and (2) sinteringthe mixture at a temperature of about 1200-1600° C. and a pressure ofabout 40-70 kbar in the presence of a bonding metal or alloy whichcomprises a combination of: (a) a first metal selected from the groupconsisting of a transition metal and a transition metal alloy; and (b)from greater than 0% up to 40% by volume of the bonding metal or alloyof a second metal which is not a carbide and is selected from the groupconsisting of aluminum, silicon, titanium, zirconium, molybdenum,niobium, tungsten, vanadium, hafnium, tantalum, chromium, magnesium,calcium, barium, yttrium, beryllium, cerium, strontium, thorium,lanthanum, and lithium, and alloys thereof; to produce the abrasiveproduct.
 39. The method of claim 38, wherein the abrasive article has acubic boron nitride content of about 10-18% by weight.
 40. The method ofclaim 38, wherein the cubic boron nitride particles have a particle sizeof less than about 20 microns.
 41. The method of claim 38, wherein thecubic boron nitride particles have a particle size of less than about 10microns.
 42. The method of claim 38, wherein the sintering is performedunder controlled non-oxidising conditions.
 43. The method of claim 38,further comprising the step of removing volatiles from the carbideparticles, cubic boron nitride particles, and bonding metal or alloyprior to sintering.
 44. The method of claim 43, wherein the volatilesare removed by applying a vacuum pressure of about 1 mbar or less at atemperature of about 500-1200° C.
 45. The method of claim 38, whereinthe bonding metal or alloy constitutes about 2-20% by weight of theabrasive product.
 46. The method of claim 38, wherein the bonding metalor alloy constitutes about 5-20% by weight of the abrasive product. 47.The method of claim 38, wherein the bonding metal or alloy constitutesless than about 15% by weight of the abrasive product.